The present invention relates to a radio communication apparatus and radio frequency correcting method thereof, and more particularly to a radio frequency correcting method for a radio communication system for producing a radio frequency synchronizing with a transmission path frequency of digital data transmitted from a wire digital transmission path and so on.
FIG. 7 is a block diagram of a structural example of a base station in a conventional radio communication system of the same sort. In FIG. 7, a digital data such as sounds, images, or texts transmitted from a switching center that is not shown in figures via a wire transmission path is inputted, the transmitted data is modulated by a preset modulating method, the modulation signal is converted into a radio frequency, and the signal is radio-transmitted to a mobile device that is not shown in the figures.
In FIG. 7, transmission path data transmitted from the switching center via a digital transmission network are inputted to a data generating portion 3 and a transmission path frequency reference clock producing portion 1. The transmission path data are, as is described above, sound, image, or text data, and are data digitized and formatted in a predetermined form.
The transmission path frequency reference clock producing portion 1 extracts a transmission timing of the transmitted digital data (a reference clock signal) from the inputted transmission path data by using a transmission timing generator 11 with a method such as clock extraction, and sends the extracted transmission timing 11a to the data generating portion 3. Moreover, the transmission timing generator 11 also sends the reference clock signal to a dividing/multiplying device 12 for implementing processes such as multiplying or dividing as the need arises. The multiplied or divided output 12a is sent to a data converter 32.
A data generating portion is composed of a data generator 31 and a dada converter 32, both for decoding the transmission path data so as to convert the data into a data system to be modulated into a radio modulation signal. The data system is outputted from the data generator 31 as digital data 31a, and is sent to the data converter 32 at a timing of the transmission timing signal 11a. The data converter 32 orthogonal-modulates the obtained digital data, converts its frequency into a radio intermediate frequency (IF frequency) (32a), and sends the data to a D/A converter 5. The D/A converter 5 produces a radio IF modulation signal 5a converted into the IF frequency on the basis of the inputted data. Although functions such as wave-shape formation or band limitation that are necessary for transmitting codes are actually added to the D/A converter 5, they are not particularly shown in the figures. The generated radio IF modulation signal 5a is inputted to a frequency converting portion 6.
A frequency converting portion 6 is composed of a local oscillator 61 to which a PLL (phase locked loop) technique is applied, a mixer 62, and a filter (BPF) 63. It produces the radio frequency signal at the mixer 62 on the basis of a local oscillation signal generated by the local oscillator 61, removes unnecessary waves from the signal by using the filter 63, and then outputs the radio frequency signal to a radio circuit.
The digital PLL technique, which can provide a frequency according to a voluntary dividing step from a reference frequency generator 21 in accordance with the inputted digital data, is applied to the local oscillator 61. The explanation thereof is omitted since the technique is well known. The local oscillator 61 produces the local oscillation signal synchronizing with the reference frequency signal 23a outputted from the reference frequency generating portion 2. The reference frequency generating portion 2 includes the reference signal generator 21 and the dividing/multiplying device 23 for dividing or multiplying the reference signal as the need arises.
In FIG. 7, a radio intermediate frequency modulation signal (radio IF modulation signal) 5a being a base of a radio modulation signal 63a is directly produced by a D/A converter 5. The signal 5a is mixed with a local oscillation frequency oscillated by a local oscillator 61 at a mixer 62, and becomes a radio modulation signal 63a. At this time, frequency stability of the radio modulation signal 63a depends on a reference signal generated by a reference frequency generator 21 and a reference signal generated by a reference clock producing portion 1 synchronizing with a clock obtained by clock-extraction from transmitted data at a transmission path.
Normally, according to the fact that the transmission path, which is sufficient to refer data during a voluntary timing, and the radio frequency, which is required to have stability based on Electric Wave Law for strongly restricting illegal radiation, are inputted and outputted respectively, it is natural that, concerning the stability of the frequencies, precision of the reference frequency generator 21 is higher than that of the transmission timing generator 11 in comparison.
According to this, the frequency stability of the radio modulation signal 63a is largely dominated by a reference clock producing portion 1 so that the frequency stability is deteriorated. It is very important point how the frequency stability of the part can be improved, or how the frequency difference can be compensated in improving the frequency stability of the radio modulation signal 63a. 
Here, it is object of the present invention to provide a radio communication apparatus that can improve the stability of the radio frequency, and a radio frequency correcting method thereof.
A radio communication apparatus according to the present invention includes:
an intermediate frequency modulation signal producing means for producing a modulation signal at an intermediate frequency out of transmitted data from a transmission path by using the first reference signal synchronizing with the data;
a radio frequency converting means for converting the intermediate frequency modulation signal into a radio frequency by using the second reference signal being more stabile than the first reference signal; and
a radio frequency correcting means for detecting a frequency difference between the first reference signal and the second reference signal, and for correction-controlling the radio frequency at the radio frequency converting means in accordance with the frequency difference.
Moreover, the radio frequency correcting means includes a means for detecting the frequency difference of the first reference signal on the basis of the second reference signal, and a means for correction-controlling a frequency of a local oscillation signal at the radio frequency converting means in accordance with the frequency difference. The intermediate frequency modulation signal producing means includes a modulating means for modulating the transmitting data with an orthogonal modulating method by using the first reference signal.
A radio communication apparatus according to the present invention includes:
a buffer means for temporarily storing transmitted data from a transmission path synchronously with the first reference signal;
a reference signal generating means for generating the second reference signal being more stabile than the first reference signal;
an intermediate frequency modulation signal producing means for reading-out data from the buffer means synchronously with the second reference signal so as to produce a modulation signal at an intermediate frequency out of the read-out data by using the second reference signal; and
a radio frequency converting means for converting the intermediate frequency modulation signal into a radio frequency by using the second reference signal. The intermediate frequency modulation signal producing means includes a modulating means for modulating the transmitted data with an orthogonal modulating method by using the second reference signal.
A radio frequency correcting method according to the present invention is for a radio communication apparatus designed so as to convert transmitted data from a transmission path into a modulation signal at an intermediate frequency by using the first reference signal synchronizing with the data, and to convert the intermediate frequency modulation signal into a radio frequency by using the second reference signal being more stabile than the first reference signal, which includes a radio frequency correcting means for detecting a frequency difference between the first reference signal and the second reference signal, and for correction-controlling the radio frequency at the radio frequency converting means in accordance with the frequency difference.
Moreover, the radio frequency correcting means includes a means for detecting the frequency difference of the first reference signal on the basis of the second reference signal, and a means for correction-controlling a frequency of a local oscillation signal for the radio frequency conversion in accordance with the frequency difference. The intermediate frequency modulation signal results from modulating the transmitted data with an orthogonal modulating method by using the second reference signal.
Another radio frequency correcting method according to the present invention is for a radio communication apparatus designed so as to convert transmitted data from a transmission path synchronous with the first reference signal into a modulation signal at an intermediate frequency, and to convert the intermediate frequency modulation signal into a radio frequency by using the second reference signal being more stabile than the first reference signal, which includes:
a buffer means for temporarily storing the transmitted data synchronously with the first reference signal;
an intermediate frequency modulation signal producing means for reading-out data from the buffer means synchronously with the second reference signal so as to produce a modulation signal at an intermediate frequency out of the read-out data by using the second reference signal; and
a radio frequency converting means for converting the intermediate frequency modulation signal into the radio frequency by using the second reference signal. The intermediate frequency modulation signal results from modulating the transmitted data with an orthogonal modulating method by using the second reference signal.
The effects of the present invention will be described. In a radio system for producing a radio carrier synchronizing with the transmission path frequency of the digital data transmitted from a wire digital transmission path and so on, an influence of the difference of the transmission path frequency that obstructs the stability of the radio carrier frequency is compensated as frequency offset of a signal transmitted from the radio station on the basis of the differential frequency by comparing the difference with the high-stability radio reference clock, and detecting the differential frequency. Moreover, as another example, the influence of the difference of the transmission path frequency is compensated by a method of temporarily accumulating by the buffer the digital data transmitted through the transmission path, and generating the radio carrier by reading out the data while re-transmitting it at the timing of the high-stability radio reference clock.